The present invention relates to an electric pump for liquid which is used as an oil pump or the like, more particularly to an improvement of an electric pump in which an outer rotor of a pump section is drivingly rotated as a rotor of a motor section.
Japanese Patent Application Publication No. 2012-67735 (Patent Literature 1) discloses a previously-proposed electric pump. In this technique, a principle of a rotation-type volume pump which is generally called “pendulum-type pump” or the like is used. Also as disclosed in Japanese Patent Application Publication No. 2015-117695 (Patent Literature 2), the pendulum-type pump includes an inner rotor and an outer rotor which are eccentric relative to each other. These inner rotor and outer rotor are connected with each other by a plurality of radially-disposed connecting plates such that the inner rotor can rotate together with the outer rotor. The plurality of connecting plates partition a crescent-shaped space formed between the inner rotor and the outer rotor, into a plurality of chambers. Hence, by rotating the inner rotor and the outer rotor, a pumping action similar to that of a vane pump can be obtained.
In the electric pump disclosed in Patent Literature 1, permanent magnets are provided on an outer circumferential surface of the outer rotor, and stator coils are provided radially outward of the outer rotor. This outer rotor cooperates with the stator coils to function as an electric motor. That is, the outer rotor which is a structural component of a pump section rotates by a direct drive in cooperation with the stator coils.
In the technique of Patent Literature 1, plate holding grooves are formed in an inner circumferential surface of the outer rotor in order to swingably support end portions of the connecting plates. Each permanent magnet is located between one pair of adjacent plate holding grooves with respect to a circumferential direction (i.e. when comparing those circumferential locations). In other words, the plate holding grooves do not overlap with the permanent magnets as viewed in a radial direction. That is, two connecting plates are located on circumferential both sides of each permanent magnet.